This invention relates to a soil levelling device to be used with an impact roller.
The term xe2x80x9cimpact rollerxe2x80x9d, as used initially in U.S. Pat. No. 2,909,106 refers to a soil compaction machine including a compactor mass of non-round shape which, when towed over a soil surface, produces a series of periodic blows on the soil surface. The compactor mass of an impact roller has a series of spaced apart, salient points on its periphery. Each such salient point is followed by compacting face with, in most cases, a re-entrant portion of the periphery between the salient point and the compacting face. As the impact roller is towed over the soil surface, for instance by means of a tractor, it rises up on each salient point and then falls forwardly and downwardly as it passes over that point, with the result that the following compacting face applies an impact blow to the soil surface. The coupling between the tractor and the compactor mass is resilient in nature to allow for the necessary forward and downward falling motion undergone by the mass as it passes over each salient point. In practice, as the compactor mass is moved over the soil surface, it produces a series of indentations in the soil surface which are spaced apart in the direction of movement of mass. The longitudinal spacing of the indentations is the same as the peripheral spacing of the compacting faces of the compactor mass. After one or several passes of the impact roller it is necessary to smooth the soil surface. This is typically done with the aid of a motor grader or, in some instances, using the blade of a bulldozer. In either case, the levelling operation requires a separate and expensive piece of equipment. Added to this the efficiency of the compaction operation is considerably reduced by the necessity for the use of levelling equipment after compaction has taken place. It has been proposed in WO 94/26985 to provide, in the case of an impact roller with two side by side compactor masses, a levelling blade arrangement which trails the compactor masses to apply a levelling action to the soil after passage of the compactor masses. With this proposal, it is possible to perform the levelling operation simultaneously with the compaction operation. It is an object of the present invention to provide a modified form of levelling device.
According to the present invention there is provided a soil levelling device for an impact roller, the levelling device comprising:
coupling means for coupling the levelling device to the impact roller so as to trail the impact roller in use;
a support frame;
at least one compactor mass;
for each compactor mass of the impact roller, a ground-engaging levelling blade fast with the support frame, the levelling blade being arranged to cut soil which has been traversed by the compactor mass and thereby to perform a soil levelling action; and
for each levelling blade, a ground-engaging shoe connected to the support frame for pivotal movement relative to the support frame about an axis transverse to the direction of movement of the impact roller, the shoe serving to control the depth of cut achieved by the levelling blade.
Means are preferably provided which are operable to vary the elevation of the, or each, levelling blade relative to the support frame.
Typically, the device of the invention will be used with an impact compactor having two compactor masses spaced transversely apart from one another, the support frame carrying two transversely spaced apart levelling blades and two transversely spaced apart, ground-engaging shoes, one levelling blade and one shoe being provided for each compactor mass. The support frame will then include a transverse beam mounted for pivotal movement about a fore-and-aft axis, the levelling blades and shoes being supported in spaced apart relationship at opposite ends of the transverse beam.
The device may also comprise lifting and lowering means operable to raise and lower the support frame relative to the soil surface traversed in use by the levelling device. The lifting and lowering means may, for instance, comprise a double-acting hydraulic cylinder acting between the coupling means and a bracket to which the transverse beam is pivoted, the pressurisation of the hydraulic cylinder determining the force with which the levelling blades are biased into engagement with the soil surface. In one embodiment of the invention, there may be an hydraulic accumulator connected to the cylinder, the hydraulic accumulator serving to damp reaction forces on the levelling blades. In another embodiment, the cylinder may act via a pressurised air bag on the bracket to which the transverse beam is pivoted, the air bag serving to damp reaction forces on the levelling blades.
In the preferred embodiments, each around-engaging shoe has fore and aft portions which respectively lead and trail the associated levelling blade. In one version of the invention, the fore and aft portions of each shoe are in the form of skid, while in another version of the invention, the fore and aft portions of each shoe are in the form of rollers or groups of rollers. According to another aspect of the present invention there is provided a method of compacting and levelling a soil surface, the method comprising the steps of coupling a levelling device according to any one of the preceding claims to an impact roller and causing the impact roller to traverse the soil surface, with the levelling device trailing behind the impact roller, so that the impact roller applies periodic compacting blows to the soil surface and the levelling device then applies a levelling action to the soil surface.